The field of the invention is nanoporous materials.
As the size of functional elements in integrated circuits decreases, complexity and interconnectivity increases. To accommodate the growing demand of interconnections in modem integrated circuits, on-chip interconnections have been developed. Such interconnections generally consist of multiple layers of metallic conductor lines embedded in a low dielectric constant material. The dielectric constant in such material has a very important influence on the performance of an integrated circuit. Materials having low dielectric constants (i.e., below 2.2) are desirable because they allow faster signal velocity and shorter cycle times. Moreover, lowering of the dielectric constant reduces capacitive effects, leading often to less cross talk between conductor lines and lower voltages to drive integrated circuits.
One way of achieving low dielectric constants is to select materials with inherently low dielectric constants. Generally, two different classes of low dielectric constant materials have been employed in recent yearsxe2x80x94inorganic oxides and organic polymers. Inorganic oxides often have dielectric constants between 2.5 and 4, which tends to become problematic when device features are smaller than 1 xcexcm. Organic polymers, including epoxy networks, cyanate ester resins and polyimides vary greatly in their usefulness as low dielectric material. Epoxy networks frequently show disadvantageously high dielectric constants at about 3.8-4.5. Cyanate ester resins have relatively low dielectric constants between approximately 2.5-3.7, but tend to be rather brittle, thereby limiting their utility. Polyimides have shown many advantageous properties including high thermal stability, ease of processing, low stress/TCE, low dielectric constant and high resistance. Polyimides are therefore frequently used as alternative low dielectric constant polymers.
Another way of achieving low dielectric constants is to introduce air into an appropriate material, since air has a dielectric constant of about 1.0. Air is usually introduced into a material by formation of minute voids (also referred to herein as pores), with a size in the sub-micrometer range. Such porous material is then usually termed xe2x80x9cnanoporous materialxe2x80x9d. It is known to produce nanoporous polymers by providing a polymer with thermolabile regions, and then thermolyzing the thermolabile regions to produce voids. Examples are set forth in U.S. Pat. No. 5,776,990 to Hedrick et al.
There are, however, technical difficulties in regulating the pore size and distribution. It is also problematic in some applications to provide a material with sufficient heat to thermolize the thermolabile portions. It is therefore desirable to provide nanometer-sized voids by another means, which does not require thermolysis.
In accordance with the present invention, compositions and methods are provided in which an electrical device is fabricated by depositing macrocycles on a substrate portion of the device, wherein the macrocycles may be part of polymeric strands, which are subsequently crosslinked to form a crosslinked polymer. Where the macrocycles are not part of the polymeric strands, the macrocycles are integrated into the crosslinked polymer by a crosslinking reaction.
In one aspect of the inventive subject matter, at least some of the macrocycles are relatively large, including at least six rings in the backbone of the macrocycles. Especially large macrocycles may have 12 or more rings in the backbone, while the rings themselves may be relatively large, preferably having at least six atoms such as in phenyl rings.
In one class of preferred embodiments, the macrocycles form part of the backbone in the polymer. In another class of preferred embodiments, the macrocycles are grafted onto the polymer, and in a third class of preferred embodiments, the macrocycles are employed in crosslinking strands of the polymer.
In yet another aspect of the inventive subject matter, intermacrocyclic links can be relatively complex. For example, two of the macrocycles may be coupled to a single atom, such as a carbon or a silicon atom. Multiple macrocycles may also be coupled to a single phenyl group. Furthermore, the macrocycles can be heavily conjugated, with more preferred macrocycles having a completely conjugated backbone, and it is preferred that the macrocycles are fabricated from a bisphenol and a difluoroaromatic compound. In still further aspects of preferred embodiments, the macrocycles can have backbones with ether, carboxyl, and ethynyl groups, some of which can be used in crosslinking without reliance on an extrinsic crosslinker.
Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawing.